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A Low-Cost Collector For Sampling Low-Volume Water Flow

By Luis Pons
March 24, 2003

Small-scale water sampling may become less expensive, and thus possible in more locations, thanks to a compact sample collector designed by Agricultural Research Service scientists.

The device collects samples of drip or low-stream flows that can be analyzed for levels of nutrients, pesticides or fine sediment. It also provides total-flow estimates for given time periods. Development of the device was led by ARS agricultural engineer Robert Malone when he was based at the ARS North Appalachian Experimental Watershed in Coshocton, Ohio.

The sample collector is small, useful in remote conditions, easy to maintain and easily constructed from readily obtainable materials. It collects about 2 percent of total flow at rates ranging from 0.01 to 3.2 gallons per hour.

Analysis of composite water samples is essential for tracking changes in chemical or sediment concentrations in surface water and groundwater. Costs, however, limit the number of sampling locations.

Few current samplers can collect, at low cost, both drip flow and continuous-streaming flow from tile drains, large soil blocks and springs. Many of the existing samplers are bulky units that are not designed for drip flow, require extensive circuitry, and cost more than $1,000.

According to Malone, his sample collector can be built for $20 to $30, although some digging and construction will sometimes be needed for field use.

The sampler, in the form of a cube measuring roughly 5 inches on each side, works by directing percolating water droplets onto a rotating lid that contains a 0.16 inch-wide slot. The slot allows water to flow down into a collection container. The rotating lid is powered by a clock-type motor.

The device should handle greater flow rates with minor modifications, according to Malone. It was designed by Malone, who now works at ARS' National Soil Tilth Laboratory in Ames, Iowa, and by hydraulic engineer James Bonta and soil biological technician Donald Lightell, both with ARS at Coshocton.

The sample collector may eventually be presented to potential marketers.

ARS is the U.S. Department of Agriculture's chief scientific research agency.